BS A 298:1988 pdf free download.Methods of test for Self-locking nuts with maximum operating temperature greater than 425 °C.
1 Scope and field of application
BS A 298 specifies test methods for metric self-locking nuts with MJ threads the maximum operating temperature of which is greater than 425 °C, intended for use in aerospace construction. It describes the test device and the method for each test.
Other test devices or test methods than those specified in BS A 298 may be used, but, in the event of a dispute, the requirements laid down in this International Standard shall take precedence.
BS A 298 shall be used in conjunction with the procurement specification laid down in ISO 8641.
It applies to self-locking nuts as defined above, provided that the relevant documents (drawing, procurement specification, etc.) refer to BS A 298.
2 References
ISO 691, Wrench and socket openings — Metric series — Tolerances for general use.
ISO/R 1024. Rockwell superficial hardness test (N and T scales) for steel.
ISO 5855-1, Aerospace construction — Mi threads — Part 1: Basic profile.
ISO 5855-2, Aerospace — MJ threads — Part 2: Dimensions of bolts and nuts,
ISO 6507-1, Metallic materials — Hardness test — Vickers test — Part 1: HV 5 to I-TV 100.
ISO 6508. Metallic materials — Hardness test — Rockwell test (scales A — B — C — D — E — F — C—H—K).
ISO 7403, Fasteners for aerospace construction — Spline drive wrenching configuration — Metric series.
ISO 8641, Aerospace — Self-locking nuts with maximum operating temperature greater than 425 °C — Procurement specification2.
3 Inspections and tests
3.1 Hardness test
3.1.1 Procedure
The authorized procedures are as follows:
— Rockwell hardness, in accordance with
ISO 6508;
— Vickers hardness, in accordance with
ISO 6507-1;
The test device includes the following elements:
a) a fixing plate;
b) a push rod with spherical end;
c) a bolt with a rolled thread and characteristics
as follows:
1) thread: in accordance with ISO 5855-1 and ISO 5855-2,
2) tensile strength classification: no particular requirement,
3) material: no particular requirement;
d) rivets with universal heads or bolts with cylindrical heads and hexagonal nuts to fix the nut or the portion of the channel to be tested (standardized aerospace fasteners).
3.6.2 Method
This test shall be carried out at ambient temperature.
Attach the nut or the portion of the channel to be tested onto the plate by means of rivets or bolts and nuts, the preformed heads of rivets or the heads of bolts being located on the same side as the element to be tested. Apply the axial load stipulated in the procurement specification using the rod with the spherical end.
Using an appropriate feeler gauge, ensure that any permanent deformation is not greater than the value stipulated in the procurement specification.
Try to screw a standard bolt manually into the nut, even if deformed, as far as the locking device. Dismantle, then subject the nut as well as the cage and the channel to a visual examination and, if necessary, to an examination under low magnification after sectioning to check conformity with the requirements of the procurement specification.
NOTE Nuts subjected to this test shall not be used again.
Remove the load by unscrewing through half a turn and cease movement. Again unscrew and measure the breakaway torque, using the same procedure.
Dismantle the assembly, then submit the bolt and nut to a visual examination and, if necessary, to an examination under low magnification after sectioning to check conformity with the requirements of the procurement specification.
3.7.2.2 Multiple cycle test
Proceed as stated in 3.7.2.1 repeating the cycle on the same bolt the number of times stipulated in the procurement specification. and measure the self-locking torque under the same conditions at the first assembly and at each disassembly. It is mandatory that the first assembly be carried out on a new bolt. Each disassembly shall be sufficient to disengage the nut locking device entirely.
NOTE Nuts subjected to the multiple cycle test shall not be used again.
3.8 Self-locking torque at ambient temperature after heat soak at maximum operating temperature
3.8.1 Test device
The test device is illustrated in Figure 9.
The test device includes the following elements:
a) a spacer in material identical to that of the nut to be tested;
b) a bolt with a rolled thread and a normal shank (diameter of the plain portion equal to the diameter of the thread) or with a reduced shank (diameter of the plain portion equal to the pitch diameter); the characteristics of the bolt are as follows:
1) thread: in accordance with ISO 5855-1 and
ISO 5855-2,
2) material: identical to that of the nut to be
tested,
3) coating: in accordance with Table 2; c) a torque wrench.
After submitting the assembly to load, leave it under tension at room temperature for at least 1 h:
measure the elongation again and, if necessary, readjust it so as to obtain the desired preload (this measurement shall be carried out with an accuracy of± I jim).
Heat the assembly to the temperature and for the length of time stipulated in the procurement specification.
Remove the assembly from the oven and allow it to cool slowly to ambient temperature.
Remove the load by unscrewing through haifa turn and cease movement. Again unscrew and measure the breakaway torque, using the torque wrench.
Stop the motion again, clean the bolt threads protruding beyond the nut to remove the baked oil residue and lubricate it with synthetic aero engine oil so as to avoid abrasive damage to the nut. Remove the nut.
Repeat the cycle the number of times stipulated in the procurement specification, the bolt being cleaned and brushed after each removal, and measure the self-locking torque at each cycle under the same conditions.
Dismantle, then submit the bolt and nut to a visual examination and, if necessary, to an examination under low magnification after sectioning to check conformity with the requirements of the procurement specification.
NOTE Nuts subjected to this test shall not be used again.
3.9 Permanent set test
This test details the method for checking the possibility of reusing self-locking nuts on bolts the thread of which is at the tolerance limit.
3.9.1 Test device The test device consists of
a) a maximum and a minimum threaded
mandrel, in conformity with Figure 10, the characteristics of which are as follows:
1) threads: in accordance with ISO 5855-1 and
ISO 5855-2, except for the pitch diameter and
tolerances which shall be in accordance with
the values specified in Table 3,
2) material: steel, heat-treated to HRC 39; b) a torque wrench.